This invention relates to the transformation of imaging data by a discrete cosine transformation and, more particularly, to the sharpening and scaling of two dimensional images by use of even and odd cosine transformations compatible with circuitry of the JPEG (Joint Photographic Expert Group) and MPEG (Motion Picture Expert Group) international compression standard.
Image processing is employed in numerous situations including electronic processing of photographic images, reconstruction of images in a printing process, and the filtering and reconstruction of images in the transmission of images in a communication system. Various techniques employed in image processing may be reviewed briefly by considering systems employed for storage and transmission of image or video data.
Systems for storage of image or video data, as well as for the transmission of image or video data are constructed generally of some form of electronic camera or electro-optic scanner for viewing a subject, followed by signal processing circuitry for transforming the signal, and/or encoding the signal to provide a format of compressed data. The compressed format of data facilitates storage by reduction of the number of data points to be stored, and facilitates transmission by reducing the number of data points to be transmitted. In the case of data transmission, by way of example, the reduction of data points permits a reduction of necessary bandwidth or an increased speed of transmission. At a receiver, the image data is retrieved by inverse transformation and/or decoding, followed by presentation on a display. Of particular interest herein is data compression by use of JPEG and/or MPEG signal processing.
By way of example, in such a video storage or video communication system, image data of a subject may be obtained with an electronic camera having a CCD (charge coupled device) array of detecting elements for detecting pixels of an image of a scene to be viewed. A two-dimensional CCD array may employ a million cells providing black and white data. Strips of filter material may be employed for detection of color in the scene being viewed. The CCDs output analog voltage pulses which may be shifted, in the manner of operation of a shift-register, to allow a succession of the pulses to provide the data serially to an analog-to-digital converter. Digital signals outputted by the analog-to-digital converter are stored for subsequent digital processing.
The digital signals are processed by electronic signal processing circuitry. Of particular interest herein, is the processing of digital signals, including digital signal transformation by use of the discrete cosine transform, as is employed by JPEG compression. While the specific area of interest herein lies in the use of the cosine transform, it is useful for the general understanding of digital signal processing, including various aspects of sampling, filtering and coding, to consider related signal processing techniques. For example, with reference to the following U.S. patents, the Walsh-Hadamard transform is mentioned in Powell, U.S. Pat. No. 4,442,454 (Abstract), and Bayer, U.S. Pat. No. 4,553,165 (Abstract). Horizontal synchronization of signals from television video including luminance Y. and chrominance I and Q components, as well as Huffman and run-length decoding and a FIFO memory are disclosed in Widergren, U.S. Pat. No. 4,302,775 (Columns 7 and 11). The Z transform is disclosed in David, U.S. Pat. No. 4,760,605 (Columns 9 and 10). Implementation of a discrete cosine transformation is disclosed Keesen, U.S. Pat. No. 4,807,033. Spatial sampling frequency is disclosed in Lake, U.S. Pat. No. 4,809,070 (Column 5).
One aspect in the use of the foregoing techniques for the transmission of pictorial data is the efficiency with which data can be stored or transmitted. For example, data compression, which may employ the counting of contiguous pixels having a common value of luminance rather than a separate storage or transmission of individual ones of the pixels, is readily implemented by the Huffman coding. Improved precision, or immunity from noise, is attained by signal transformation such as the discrete cosine transformation. It is noted, however, that the electrical circuitry employed for accomplishing these functions, such as the discrete cosine transformer is very complex.
There are other functions which can also be applied in the utilization of pictorial data, such as the functions of sharpening an image or scaling an image. Sharpening refers to enhancement or an image by accentuation of boundaries of objects in the image, as by increasing amplitudes of higher-frequency components of the image to counteract a reduction of the amplitudes of higher-frequency components which may have occurred during transmission of the image. Scaling is used in the sense of resampling to alter the number of pixels in a line of pixels so as to enable presentation of an image on a display having a different number of pixels per line than is present in the array of detectors which forms the original image. Heretofore, such additional functions have been accomplished by the use of additional circuitry, such as filter circuits for sharpening an image and a resampling system for scaling an image.
A problem arises in that there has been a necessity for employing the additional circuitry for accomplishing the additional functions even though there is circuitry, namely, the circuitry of the discrete cosine transformer which, due to its great operating speed, can be used for a multifunctional capacity. Array transform circuitry of the discrete cosine transformer is employed for data compression in a JPEG compression system, and provides both the discrete cosine transform (DCT) and the inverse discrete cosine transform (IDCT).